Hydraulic shovels carry out what may be termed horizontal levelling work and the like using a bucket. When carrying out such horizontal levelling work and the like, it is desirable that the bucket blade tip moves automatically, and that the range of movement of the bucket blade tip is as wide as possible.
Thus, devices which control the path of movement of the blade tips of buckets on hydraulic shovels have already been the subject of various patent applications.
For example, Published Japanese Patent Application Sho. 54-37406 discloses a device which automatically excavates in a straight-line, but even though this device eliminates the tiresomeness of manual operation, it does entail problems in that it is arranged in such a way that the automatic operation is stopped whenever the drive shaft of any of a boom or arm, etc. reaches the end of its stroke, and the range of movement of the bucket blade tip under automatic operation is limited by the stroke of the working machine. For example, if a bucket 6 is moved in a pushing direction as illustrated by the arrow I in FIG. 9, and the blade tip 6b of the bucket 6 reaches the position B, then the hydraulic cylinder 8 for the second arm 4 will arrive at the end of its extension stroke, and at this point it automatically stops. In this case, the working area is over a narrow range in the zone C-B.
Further, Laid-open Japanese Patent Application Sho. 63-65507 discloses a technique whereby an operator inputs restricting conditions apply during automatic control of the path of movement of the bucket blade tip and the drive shaft is automatically selected in accordance with the restricting conditions which are input.
However, even assuming that the operator is experienced, he will not always be able to input the right restricting conditions and there are cases where the control will not be accurate. There are also problems in that, similar to the device in the Japanese patent document mentioned above, the working machine will stop when the drive shaft reaches the end of its stroke during its work, other restricting conditions have to be re-input to achieve any further movement and the continuity of the work is interrupted.
The present invention has taken this situation into account, and aims to provide a control device which is able to control the movement of the tools of working machines continuously and over a wide range, and which is able to move the tools of working machines accurately along a desired path.